What affects Memory Usage in Hosting?
 

I register for a hosting service and it have 512Mb of RAM. I wonder what affects this. thank you

High traffic affects mostly your processor time. If my hosting plan you mean shared hosting, then you will have limited minutes of processor time per day.

My advice is, if you expect high traffic, get a cloud hosting. It is relatively cheap easy to scale. Look for AWS, DigitalOcean, Linode, Rackspace etc.

The main driver for memory usage in this case would be processes that contain multiple threads. If you have a lot of processes to support additional bandwidth (I.E. Service and interrupt calls, global caching, cookies processing and storage, multiple network interfaces, advanced NAT table, DNS lookups, proxies, etc.) then the network traffic will definitely use more memory or at least require more memory for optimal performance.